Method for making an improved aluminum alloy sheet product

ABSTRACT

An aluminum alloy sheet and a method for producing an aluminum alloy sheet. The aluminum alloy sheet is useful for forming into drawn and ironed container bodies. The sheet preferably has an after-bake yield strength of at least about 37 ksi and an elongation of at least about 2 percent. Preferably, the sheet also has earing of less than about 2 percent.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The-present application is a continuation-in-part of U.S. patentapplication Ser. No. 08/401,418 filed Mar. 9, 1995, the disclosure ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to aluminum alloy sheetand methods for making aluminum alloy sheet. Specifically, the presentinvention relates to aluminum alloy sheet and methods for makingaluminum alloy sheet wherein the sheet is particularly useful forforming into drawn and ironed container bodies.

BACKGROUND OF THE INVENTION

[0003] Aluminum beverage containers are generally made in two pieces,one piece forming the container sidewalls and bottom (referred to hereinas a “container body”) and a second piece forming the container top.Container bodies are formed by methods well known in the art. Generally,the container body is fabricated by forming a cup from a circular blankof aluminum sheet and then extending and thinning the sidewalls bypassing the cup through a series of dies having progressively smallerbore size. This process is referred to as “drawing and ironing” thecontainer body.

[0004] A common aluminum alloy used to produce container bodies is AA3004, an alloy registered with the Aluminum Association. The physicalcharacteristics of AA 3004 are appropriate for drawing and ironingcontainer bodies due primarily to the relatively low magnesium (Mg) andmanganese (Mn) content of the alloy. A desirable characteristic of AA3004 is that the amount of work hardening imparted to the aluminum sheetduring the can making process is relatively minor.

[0005] Aluminum alloy sheet is most commonly produced by an ingotcasting process. In this process, the aluminum alloy material isinitially cast into an ingot, for example having a thickness of fromabout 20 to 30 inches. The ingot is then homogenized by heating to anelevated temperature, which is typically 1075° F. to 1150° F., for anextended period of time, such as from about 6 to 24 hours. Thehomogenized ingot is then hot rolled in a series of passes to reduce thethickness of the ingot. The hot rolled sheet is then cold rolled to thedesired final gauge.

[0006] Despite the widespread use of ingot casting, there are numerousadvantages to producing aluminum alloy sheet by continuously castingmolten metal. In a continuous casting process, molten metal iscontinuously cast directly into a relatively long thin slab and the castslab is then hot rolled and cold rolled to produce a finished product.However, not all alloys can be readily cast using a continuous castingprocess into aluminum sheet that is suitable for forming operations,such as for making drawn and ironed container bodies.

[0007] Attempts have been made to continuously cast AA 3004 alloy. Forexample, in a paper entitled “Production of Continuous Cast Can BodyStock,” which was presented by McAuliffe, an employee of the assignee ofthe present application, on Feb. 27, 1989, at the AIME meeting in LasVegas, it is disclosed that limited testing was conducted with twomanufacturers of 12 ounce, 90 pound cans (i.e., a minimum bucklestrength of 90 p.s.i.). One test produced 3004 can stock. The paperdiscloses that “[b]oth tests, in the 2-3% earing range, verified thatthe surface and internal quality and structure were sufficient toproduce cans of acceptable quality.” However, it has been found that thecontinuously cast AA 3004 alloy is unsuitable for typical highcarbonation beverages, such as soda, because it has insufficient bucklestrength when employed using current typical stock gauges (e.g., fromabout 0.0112″ to 0.0118″) as opposed to stock gauges used at the time ofthe McAuliffe article ( e.g., from about 0.0124″ to 0.0128″). This isdue to the poor after-bake characteristics of continuously cast AA 3004alloy that is produced having suitable earing levels. This is discussedin more detail hereinafter in connection with examples of thephysical-characteristics of continuously cast AA 3004 alloy.

[0008] U.S. Pat. No. 4,238,248 by Gyongos et al. discloses casting an AA3004 type alloy in a block casting apparatus. The alloy had a magnesiumcontent from 0.8 to 1.3 percent and a manganese content from 1.0 to 1.5percent, with up to 0.25 percent copper. As used throughout the presentspecification, all percentages refer to weight percent unless otherwiseindicated. However, there is no disclosure of processing the cast stripinto sheet suitable for container bodies.

[0009] U.S. Pat. No. 4,235,646 by Neufeld et al. describes thecontinuous casting of an AA 5017 aluminum alloy that is useful forbeverage container bodies and container ends. The alloy includes 0.4 to1.0 percent manganese, 1.3 to 2.5 percent magnesium and 0.05 to 0.4percent copper. However, it is also disclosed that “copper and iron areincluded in the present composition due to their inevitable presence inconsumer scrap. The presence of copper between 0.05 and 0.2 percent alsoenhances the low earing properties and adds to the strength of thepresent alloy.” In Examples 1- 3, the copper content of the alloys was0.04 percent and 0.09 percent. In addition, the process includes a flashanneal step. In one example, the sheet stock disclosed by Neufeld et al.had a yield strength after cold rolling of 278 MPa (40.3 ksi) and anearing percentage of 1.2 percent.

[0010] U.S. Pat. No. 4,976,790 by McAuliffe et al. discloses a processfor casting aluminum alloys using a block-type strip caster. The processincludes the steps of continuously casting an aluminum alloy strip andthereafter introducing the strip into a hot mill at a temperature offrom about 880° F. to 1000° F. (471° C.-538° C.). The strip is hotrolled to reduce the thickness by at least 70 percent and the stripexits the hot roll at a temperature of no greater than 650° F. (343°C.). The strip is then coiled to anneal at 600° F. to 800° F. (316°C-427° C.) and is then cold rolled, annealed and subjected to furthercold rolling to optimize the balance between the 450 earing and theyield strength. The preferred annealing temperature after cold rollingis 695° F. to 705° F. (368° C.-374° C.).

[0011] U.S. Pat. No. 4,517,034 by Merchant et al. describes a method forcontinuously casting a modified AA 3004 alloy composition which includes0.1 to 0.4 percent chromium. The sheet stock has an earing percentage of3.12 percent or higher.

[0012] U.S. Pat. No. 4,526,625 by Merchant et al. also describes amethod for continuously casting an AA 3004 alloy composition which isalleged to be suitable for drawn and ironed container bodies. Theprocess includes the steps of continuously casting an alloy,homogenizing the cast alloy sheet at 950° F.-1150° F. (510° C.-621° C.),cold rolling the sheet, and annealing the sheet at 350° F.-550° F. (177°C.-288° C.) for a time of about 2-6 hours. The sheet is then cold rolledand reheated to recrystallize the grain structure at 600° F.-900° F.(316° C.-482° C.) for about 1-4 hours. The sheet is then cold rolled tofinal gauge. The reported earing for the sheet is about 3 percent orhigher.

[0013] U.S. Pat. No. 5,192,378 by Doherty et al. discloses a process formaking an aluminum alloy sheet useful for forming into container bodies.The aluminum alloy includes 1.1-1.7 percent magnesium, 0.5-1.2 percentmanganese and 0.3-0.6 percent copper. The cast ingot is homogenized at900° F.-1080° F. for about 4 hours, hot rolled, annealed at 500° F.-700°F., cold rolled and then annealed at 750-1050° F. The body stock canhave a yield strength of 40-52 ksi after the final cold rolling.

[0014] U.S. Pat. No. 4,111,721 by Hitchler et al. discloses a processfor continuously casting AA 3004 type alloys. The cast sheet is held ata temperature of at least about 900° F. (482° C.) for from about 4 to 24hours prior to final cold reduction.

[0015] European Patent Application No. 93304426.5 discloses a method andapparatus for continuously casting aluminum alloy sheet. It is disclosedthat an aluminum alloy having 0.93 percent manganese, 1.09 percentmagnesium and 0.42 percent copper and 0.48 percent iron was cast into astrip. The composition was hot rolled in two passes and then solutionheat treated continuously for 3 seconds at 1000° F. (538° C.), quenchedand cold rolled to final gauge. Can bodies made from the sheet had anearing of 2.8 percent, a tensile yield strength of 43.6 ksi (301 MPa).An important aspect of the invention disclosed in European PatentApplication No. 93304426.5 is that the continuously cast strip besubjected to solution heat treating immediately after hot rollingwithout intermediate cooling, followed by a rapid quench. In fact, it isillustrated in Example 4 that strength is lost when the solution heattreatment and quenching steps of the invention are replaced with aconventional batch coil annealing cycle and cold working is limited toabout 50 percent to maintain required earing, as is typical incontinuous cast processes. Solution heat treating is disadvantageousbecause of the high capital cost of the necessary equipment and theincreased energy requirements.

[0016] There remains a need for a process which produces an aluminumalloy sheet having sufficient strength and formability characteristicsto be easily made into drawn and ironed beverage containers. The sheetstock should have good strength and elongation, and the resultingcontainer bodies should have low earing.

[0017] It would be desirable to have a continuous aluminum castingprocess in which there is no need for a heat soak homogenization step.It would be advantageous to have a continuously cast process in which itis unnecessary to continuously anneal and solution heat treat the caststrip immediately following hot rolling (e.g., without intermediatecooling) followed by immediate quenching. It would be advantageous tohave an aluminum alloy suitable for continuous casting in which thegrain size is sufficient to provide for enhanced formability. It wouldbe desirable to have an aluminum alloy suitable for continuous castingin which the magnesium level is kept low in order to achieve comparablebrightness when compared to commercially available continuous cast canstock. It would be desirable to have an aluminum alloy suitable forcontinuous casting which can be formed into containers having suitableformability and having low earing and suitable strength.

SUMMARY OF THE INVENTION

[0018] In accordance with the present invention, a method is providedfor fabricating an aluminum sheet product. The method includes thefollowing steps. An aluminum alloy melt is formed which includes fromabout 0.7 to about 1.3 weight percent manganese, from about 1.0 to about1.5 weight percent magnesium, from about 0.3 to about 0.6 weight percentcopper, up to about 0.5 weight percent silicon, and from about 0.3 toabout 0.7 weight percent iron, the balance being aluminum and incidentaladditional materials and impurities. In a preferred embodiment, thealuminum alloy melt includes from about 1.15 to about 1.45 weightpercent magnesium and more preferably from about 1.2 to about 1.4 weightpercent magnesium, from about 0.75 to about 1.2 weight percent manganeseand more preferably from about 0.8 to about 1.1 weight percentmanganese, from about 0.35 to about 0.5 weight percent copper and morepreferably from about 0.38 to about 0.45 weight percent copper, fromabout 0.4 to about 0.65 weight percent iron and more preferably fromabout 0.50 to about 0.60 weight percent iron, and from about 0.13 toabout 0.25 weight percent silicon, with the balance being aluminum andincidental additional materials and impurities. The alloy melt iscontinuously cast to form a cast strip and the.cast strip is hot rolledto reduce the thickness and form a hot rolled strip. The hot rolledstrip can be subsequently cold rolled without any intervening hot millanneal step or can be annealed after hot rolling for at least about 0.5hours at a temperature from about 700° F. to about 900° F. to form a hotmill annealed strip. The hot rolled strip or hot mill annealed strip iscold rolled to form a cold rolled strip wherein the thickness of thestrip is reduced to the desired intermediate anneal gauge, preferably byabout 35% to about 60% per pass. The cold rolled strip is annealed toform an intermediate cold mill annealed strip. The intermediate coldmill annealed strip is subjected to further cold rolling to reduce thethickness of the strip and form aluminum alloy strip stock.

[0019] In accordance with the present invention, aluminum alloy stripstock is provided comprising from about 0.7 to about 1.3 weight percentmanganese, from about 1.0 to about 1.5 weight percent magnesium, fromabout 0.38 to about 0.45 weight percent copper, from about 0.50 to about0.60 weight percent iron and up to about 0.5 weight silicon, with thebalance being aluminum and incidental additional materials andimpurities. The aluminum alloy strip stock is preferably made bycontinuous casting, Preferably, the strip stock has a final gaugeafter-bake yield strength of at least about 37 ksi, more preferably atleast about 38 ksi and more preferably at least about 40 ksi. The stripstock preferably has an earing of less than 2 percent and morepreferably less than 1.8 percent.

[0020] In accordance with the present invention, a continuous processfor producing aluminum sheet is provided. In accordance with theprocess, relatively high reductions in gauge can be achieved in both thehot mill and cold mill. Additionally, due to the fact that greater hotmill and cold mill reductions are possible, the number of hot roll andcold roll passes can be reduced as compared to commercially availablecontinuously cast can body stock. A relatively high proportion of coldwork is needed to produce can body stock having acceptable physicalproperties according to the sheet production process of the presentinvention, as compared to commercially available continuously cast canbody stock. Thus, a reduced amount of work hardening is imparted to thesheet when it is manufactured into items such as drawn and ironedcontainers, when compared to commercially available continuously castcan body stock.

[0021] In accordance with the present invention, the need for a hightemperature soak (i.e., homogenization) can be avoided. When the hightemperature homogenization step is performed when the metal is coiled,it can result in pressure welding such that it is impossible to unrollthe coil. Also, the need for solution heat treatment after the hot mill(e.g., as disclosed in European Patent Application No. 93304426.5) canbe avoided. By avoiding solution heat treatment, the continuous castingprocess is more economical and results in fewer process controlproblems.

[0022] In accordance with the present process, high amounts of recycledaluminum can be advantageously employed. For example, 75 percent andpreferably up to 95 percent or more of used beverage containers (UBC)can be employed to produce the continuous cast sheet of the presentinvention. The use of increased amounts of UBC significantly reduces thecost associated with producing the aluminum sheet.

[0023] In accordance with the present invention, a continuous cast alloyis provided which includes relatively high levels of copper (e.g., 0.3to 0.6 percent). It has surprisingly been found that the copper can beincreased to these levels without negatively affecting the earing. Ifcopper is increased in ingot cast processes, the resulting alloy can betoo strong for can-making applications. In addition, in accordance withthe present invention, relatively low levels of magnesium are used(e.g., 1.0 to 1.5 percent), leading to better can surface finish thancommercially available continuously cast can body stock. For example,when drawn and ironed cans manufactured from aluminum sheet according tothe present invention are subjected to industrial washing, less surfaceetching takes place and, therefore, a brighter can results. Also, therelatively low magnesium content decreases the work hardening rate. Alsoin accordance with the present invention, a relatively high iron contentcompared to commercially available continuous cast can body stock isemployed to increase formability. It is believed that formability isincreased because the increased iron changes the microstructureresulting in a finer grain material, when compared to a low iron contentcontinuously cast material. The tolerance of these high iron levels alsoincreases the amount of UBC that can be utilized, since iron is a commoncontaminant in consumer scrap.

[0024] In accordance with yet another embodiment of the presentinvention, a method is provided for fabricating an aluminum sheetproduct in which the initial cold rolling step is performed in theabsence of an annealing step after hot rolling and before the first coldrolling step. An annealing step is performed after the first coldrolling step, and another annealing step is performed after thesubsequent cold rolling step. The method includes the steps of:

[0025] (i) forming an aluminum alloy melt;

[0026] (ii) continuously casting the alloy melt to form a cast strip;

[0027] (iii) hot rolling the cast strip to form a hot rolled sheet;

[0028] (iv) cooling the hot rolled sheet to a temperature below therecrystallization temperature of the hot rolled sheet;

[0029] (v) cold rolling the hot rolled sheet to form a cold rolledsheet;

[0030] (vi) annealing the cold rolled sheet to form an intermediate coldmill annealed sheet; and

[0031] (vii) further cold rolling the intermediate cold mill sheet toform a further cold rolled sheet;

[0032] (viii) further annealing the further cold rolled sheet to form afurther cold mill annealed sheet;

[0033] (ix) further cold rolling the further cold mill annealed sheet toreduce the thickness of the sheet and form aluminum alloy sheet.

[0034] The elimination of the annealing step directly after the hotrolling step and the performance of two separate annealing steps onlyafter cold rolling steps offer a number of advantages, particularly whenthe resulting sheet is employed in the fabrication of containers such ascans. The containers produced from the aluminum alloy sheet can have areduced degree of earing and a reduction in the occurrence of splitflanges and sidewalls in containers produced from the sheet. The plugdiameter can be within an acceptable tolerance of the specified plugdiameter. Containers produced from the sheet can have a significantlyreduced incidence of bulging in the container necked/flange sidewallscompared to containers produced from aluminum alloy sheet havingdifferent compositions and/or produced by other processes. - It isbelieved that the alloy sheet of the present invention typicallyexperiences less work hardening during fabrication of containers fromthe sheet than other continuously cast alloys and comparable to directchill or ingot cast sheet. For instance, work hardening can occur whencans come off the canmaker and are heated to elevated temperatures todry the paint on the can. Finally, the annealing of a thinner gauge ofsheet (i.e., annealing which is performed only after cold rolling steps)compared to annealing in previous embodiments (i.e., which is performedafter casting and before hot rolling and again after cold rolling)increases the amount of reduction which can be satisfactorily achievedwith each cold roll pass and thus can eliminate one or more cold rollingpasses relative to previous embodiments.

[0035] The aluminum alloy sheet produced by the above-described methodcan have a number of desirable properties, especially for can makingapplications. By way of example, the sheet can have an as-rolledultimate tensile strength of at least about 42.5 ksi; an as-rolled yieldtensile strength of at least about 38.5 ksi; an earing ranging of nomore than about 2.0%; and/or an as-rolled elongation of more than about4%.

[0036] While not wishing to be bound by any theory, it is believed thatthe cold rolling of the hot rolled sheet before the first annealing stepto inhibit the realization of full hard properties in the sheet duringfabrication to allow inhibit the realization of full hard properties inthe sheet during fabrication is an important factor in the improvedproperties, particularly reduced earing. Prior art processes employ anannealing step following hot rolling and before the first cold rollingstep and another annealing step after one or more cold rolling steps andtypically before cold rolling to form the finished aluminum alloy sheet.The percent reduction in the gauge of the sheet from cold rollingbetween the hot mill and cold mill annealing steps in the prior artcontinuous casting processes is significantly more than the percentreduction in sheet gauge between the cold mill annealing steps in theprocess of the present invention which can cause the sheet to have fullhard properties. In contrast, the present invention maintains total coldmill reductions before the first anneal step, between the first andsecond anneal steps, and after the second anneal-step to no more thanabout 6% to prevent the sheet from acquiring full hard properties.Because of the relatively fine grain size of continuously cast sheetcompared to direct chill cast sheet, continuously cast sheet has asignificantly higher rate of increase in earing for a given percentreduction in the cold mill. The use of the first and second annealingsteps after cold milling decreases the earing to a relatively low figureand thereby maintains the sheet properties below the full hardproperties. The placement of the first annealing step following coldrolling and not hot rolling is contrary to conventional metallurgicalwisdom which teaches that the annealing and softening of the metalbefore cold milling is performed places the metal in a more uniformcondition for the cold milling.

[0037] In another embodiment of the present invention, aluminum alloysheet includes (a) from about 0.7 to about 1.3 wt % manganese; (b) fromabout 1.0 to about 1.6 wt % magnesium; (c) from about 0.3 to about 0.6wt % copper; (d) no more than about 0.5 wt % silicon; and (e) from about0.3 to about 0.7 wt % iron. The balance is aluminum and incidentaladditional materials and impurities. This alloy is particularly usefulfor aluminum alloy sheet fabricated by any of the above processes.

[0038] In another embodiment of the present invention, aluminum alloycomprises (a) from about 1.05 to about 1.07 wt % manganese, (b) fromabout 1.35 to about 1.50 wt % magnesium, (c) from about 0.45 to about0.55 wt %. copper, (d) from about 0.39 to about 0.45 wt % silicon, and(e) from about 0.55 to about 0.60 wt % iron, with the balance beingaluminum and incidental additional materials and impurities. Thealuminum alloy sheet is preferably made by continuous casting and morepreferably by any of the processes described above. Preferably, thesheet has an after-bake yield tensile strength of at least about 37.0ksi, more preferably at least about 38.0 ksi and more preferably atleast about 39.0 ksi. The sheet preferably has an earing of less thanabout 2.0%, more preferably less than about 1.8% and most preferably nomore than about 1.6%. The sheet preferably has an elongation of morethan about 4% and more preferably more than about 4.5%. Finally, thesheet preferably has an after-bake ultimate tensile strength of at leastabout 42.5 ksi, more preferably at least about 43.0 ksi and morepreferably at least about 43.5 ksi.

[0039] The aluminum alloy sheet of this embodiment can provide severaladvantages relative to aluminum alloy sheet having other compositions,especially in the fabrication of containers. The physical properties ofthe sheet of this embodiment can experience significantly less reductionduring fabrication relative to the reduction in physical properties ofother alloy sheets during fabrication. In canmaking applications, forexample, existing continuously cast alloy sheets can suffer a reductionin physical properties of as much as 4 lbs or more in buckle strengthand 20 lbs-or more in column strength, after heating the sheet indeco/IBO ovens.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a block diagram illustrating one embodiment of processof the present invention.

[0041]FIG. 2 is a block diagram illustrating another embodiment of aprocess of the present invention.

DETAILED DESCRIPTION

[0042] In accordance with the present invention, aluminum sheet havinggood strength and forming properties is provided. In addition, a processfor producing aluminum sheet is also provided. The resulting aluminumsheet is particularly suitable for the fabrication of drawn and ironedarticles, such as containers. The resulting sheet has reduced earing andimproved strength in thinner gauges than comparable sheet fabricatedaccording to the prior art.

[0043] The preferred aluminum alloy composition according to the presentinvention includes the following constituents: (1) manganese, preferablywith a minimum of at least about 0.7 percent manganese and morepreferably with a minimum of at least about 0.75 percent manganese andmore preferably with a minimum of at least about 0.8 percent manganese,and preferably with a maximum of at most about 1.3 percent manganese andmore preferably with a-maximum of at most about 1.2 percent manganeseand more preferably with a maximum of at most about 1.1 percentmanganese; (2) magnesium, preferably with a minimum of at least about1.0 percent magnesium and more preferably with a minimum of at leastabout 1.15 percent magnesium and more preferably with a minimum of atleast about 1.2 percent magnesium, and preferably with a maximum of atmost about 1.5 percent magnesium and more preferably with a maximum ofat most about 1.45 percent magnesium and more preferably with a maximumof at most about 1.4 percent magnesium; (3) copper, preferably with aminimum of at least about 0.3 percent copper and more preferably with aminimum of at least about 0.35 percent copper and more preferably with aminimum of at least about 0.38 percent copper, and preferably with amaximum of at most about 0.6 percent copper and more preferably with amaximum of at most about 0.5 percent copper and more preferably with amaximum of at most about 0.45 percent copper; (4) iron, preferably witha minimum of at least about 0.3 percent iron and more preferably with aminimum of at least about 0.4 percent iron and more preferably with aminimum of at least about 0.50 percent iron, and preferably with amaximum of at most about 0.7 percent iron and more preferably with amaximum of at most about 0.65 percent iron and more preferably with amaximum of at most about 0.60 percent iron; (5) silicon, preferably witha minimum of 0 percent silicon and more preferably with a minimum of atleast about 0.13 percent silicon, and preferably with a maximum of atmost about 0.5 percent silicon and more preferably with a maximum of atmost about 0.25 percent silicon. The balance of the alloy compositionconsists essentially of aluminum and incidental additional materials andimpurities. The incidental additional materials and impurities arepreferably limited to about 0.05 weight percent each, and the sum totalof all incidental additional materials and impurities preferably doesnot exceed about 0.15 percent.

[0044] While not wishing to be bound by any theory, it is believed thatthe copper content of the alloy composition according to the present.invention, particularly in combination with the process steps discussedbelow, contributes to the increased strength of the aluminum alloy sheetstock while maintaining acceptable elongation and earingcharacteristics. Additionally, it is believed that the relatively lowlevel of magnesium results in a brighter finish in containersmanufactured from the alloy of the present invention, due to a decreasein surface etching, when compared to currently commercially availablecontinuously cast stock. Furthermore, it is believed that the relativelyhigh level of iron leads to increased formability because the ironchanges the microstructure resulting in a finer grain material whencompared to continuous cast materials cast with similar levels ofmanganese, copper and magnesium and, having lower levels of iron.

[0045] According to a preferred embodiment of the present invention, acontinuous casting process is used to form an aluminum alloy melt intoan aluminum alloy sheet product. The continuous casting process which isshown in FIG. 1 can employ a variety of continuous casters, such as abelt caster or a roll caster. Preferably, the continuous casting processincludes the use of a block caster for casting the aluminum alloy meltinto a sheet. The block caster is preferably of the type disclosed inU.S. Pat. Nos. 3,709,281; 3,744,545; 3,747,666; 3,759,313 and 3,774,670all of which are incorporated herein by reference in their entirety.

[0046] According to this embodiment of the present invention, a melt ofthe aluminum alloy composition described above is formed. The alloycomposition according to the present invention can be formed in partfrom scrap material such as plant scrap, can scrap and consumer scrap.Plant scrap can include ingot scalpings, rolled strip slicings and otheralloy trim produced in the mill operation. Can scrap can include scrapproduced as a result of earing and galling during can manufacture.Consumer scrap can include containers recycled by users of beveragecontainers. It is preferred to maximize the amount of scrap used to formthe alloy melt and preferably the alloy composition according to thepresent invention is formed with at least about 75 percent andpreferably at least about 95 percent total scrap.

[0047] In order to come within the preferred elemental ranges of thepresent alloy, it is necessary to adjust the melt. This may be carriedout by adding elemental metal; such as magnesium or manganese, or byadding unalloyed aluminum to the melt composition to dilute excessalloying elements.

[0048] The metal is charged into a furnace and is heated to atemperature of about 1385° F. to thoroughly melt the metal. The alloy istreated to remove materials such as dissolved hydrogen and non-metallicinclusions which would impair casting of the alloy and the quality ofthe finished sheet. The alloy can also be filtered to further removenon-metallic inclusions from the melt.

[0049] The melt is then cast through a nozzle and into the castingcavity. The nozzle is typically fabricated from a refractory materialand provides a passage from the melt to the caster wherein the moltenmetal is constrained by a long narrow tip upon exiting the nozzle. Forexample, a nozzle tip having a thickness of from about 10 to about 25millimeters and a width of from about 254 millimeters to about 2160millimeters can be used. The melt exits the tip and is received in acasting cavity formed by opposite pairs of rotating chill blocks.

[0050] The metal cools as it travels within the casting cavity andsolidifies by transferring heat to the chill blocks until the stripexits the casting cavity. At the end of the casting cavity, the chillblocks separate from the cast strip and travel to a cooler where thechill blocks are cooled. The rate of cooling as the cast strip passesthrough the casting cavity of the casting apparatus is a function ofvarious process and product parameters. These parameters include thecomposition of the material being cast, the strip gauge, the chill blockmaterial, the length of the casting cavity, the casting speed and theefficiency of the block cooling system.

[0051] It is preferred that the cast strip exiting the block caster beas thin as possible to minimize subsequent working of the strip.Normally, a limiting factor in obtaining minimum strip thickness is thethickness and width of the distributor tip of the caster. In thepreferred embodiment of the present invention, the strip is cast at athickness of from about 12.5 millimeters to about 25.4 millimeters andmore preferably about 19 millimeters.

[0052] Upon exiting the caster, the cast strip is then subjected to hotrolling in a hot mill. A hot mill includes one or more pairs ofoppositely rotating rollers having a gap therebetween that reduce thethickness of the strip as it passes through the gap. The cast strippreferably enters the hot mill at a temperature in the range of fromabout 850° F. to about 1050° F. According to the process of the presentinvention, the hot mill preferably reduces the thickness of the strip byat least about 70 percent and more preferably by at least about 80percent. In a preferred embodiment, the hot mill includes 2 pairs of hotrollers and the percentage reduction in the hot mill is maximized. Thehot rolled strip preferably exits the hot mill at a temperature in therange from about 500° F. to about 750° F. In accordance with the presentinvention, it has been found that a relatively high reduction in gaugecan take place in each pass of the hot rollers and therefore the numberof pairs of hot rollers can be minimized.

[0053] The hot rolled strip is optionally annealed to remove anyresidual cold work resulting from the hot mill operation and to reducethe earing. Preferably, the hot rolled strip is annealed in a hot millanneal step at a temperature of a minimum of at least about 700° F. andmore preferably a minimum of at least about 800° F., and preferably witha maximum temperature of at most about 900° F. and more preferably amaximum temperature of at most about 850° F. According to oneembodiment, a preferred temperature for annealing is about 825° F. Theentire metal strip should preferably be at the annealing temperature forat least about 0.5 hours, more preferably at least about 1 hour and morepreferably at least about 2 hours. The amount of time that the entiremetal strip should be at the annealing temperature should preferably bea maximum of at most about 5 hours, more preferably a maximum of at mostabout 4 hours. In a preferred embodiment, the anneal time is about 3hours. For example, the strip can be coiled, placed in an annealingfurnace, and held at the desired anneal temperature for from about 2 toabout 4 hours. This length of time insures that interior portions of thecoiled strip reach the desired annealing temperature and are held atthat temperature for the preferred period of time. It is to be expresslyunderstood that the annealing times listed above are the times for whichthe entire metal strip is maintained at the annealing temperatures, andthese times do not include the heat-up time to reach the annealtemperature and the cool-down time after the anneal soak. The coiledstrip is preferably cooled expeditiously to allow further processing,but is not rapidly quenched to retain a solution heat treated structure.

[0054] Alternatively, the hot rolled strip is not subjected to a hotmill anneal step. In this alternative embodiment, the hot rolled stripis allowed to cool and is subsequently subjected to cold rolling withoutany intermediate thermal treatment. It is to be expressly understoodthat the hot rolled strip is not subjected to a heat soakhomogenization, nor is it subjected to a solution heat treatmentfollowed by a rapid quench. The strip is cooled in the manner that ismost convenient.

[0055] After the hot mill annealed or hot rolled sheet has cooled toambient temperature, it is cold rolled in a first cold rolling step toan intermediate gauge. Preferably, cold rolling to intermediate gaugeincludes the step of passing the sheet between one or more pairs ofrotating cold rollers (preferably 1 to 3 pairs of cold rollers) toreduce the thickness of the strip by from about 35 percent to about 60percent per pass through each pair of rollers, more preferably by fromabout 45 percent to about 55 percent per pass. The total reduction inthickness is preferably from about 45 to about 85 percent. In accordancewith the process of the present invention, it has been found that arelatively large reduction in the gauge of the aluminum sheet can takeplace in each pass as compared to a commercially available continuouslycast can stock. In this manner, it is possible to reduce the number ofpasses required in the cold mill.

[0056] When the desired intermediate anneal gauge is reached followingthe first cold rolling step, the sheet is intermediate cold millannealed to reduce the residual cold work and lower the earing.Preferably, the sheet is intermediate cold mill annealed at a minimumtemperature of at least about 600° F., more preferably at a minimumtemperature of at least about 650° F., and preferably at a maximumtemperature of no more than about 900° F. and more preferably at amaximum temperature of no more than about 750° F. According to oneembodiment, a preferred annealing temperature is about 705° F. Theanneal time is preferably a minimum of at least about 0.5 hours and ismore preferably a minimum of at least about 2 hours. According to oneembodiment of the present invention, the intermediate cold mill annealstep can include a continuous anneal, preferably at a temperature offrom about 800° F. to about 1050° F. and more preferably at atemperature of about 900° F. It has unexpectedly been found that thesecold mill annealing temperatures lead to advantageous properties.

[0057] After the cold rolled and intermediate cold mill annealed sheethas cooled to ambient temperature, a final cold rolling step is used toimpart the final properties to the sheet. The preferred final cold workpercentage is that point at which a balance between the ultimate tensilestrength and the earing is obtained. This point can be determined for aparticular alloy composition by plotting the ultimate tensile strengthand earing values against the cold work percentage. Once this preferredcold work percentage is determined for the final cold rolling step, thegauge of the sheet during the intermediate annealing stage and,consequently, the cold work percentage for the first cold roll step canbe determined and the hot mill gauge can be optimized to minimize thenumber of passes.

[0058] In a preferred embodiment the reduction to final gauge is fromabout 45 to about 80 percent, preferably in one or two passes of fromabout 25 to about 65 percent per pass, and more preferably a single passof 60 percent reduction. When the sheet is fabricated for drawn andironed container bodies, the final gauge can be, for example, from about0.0096 inches to about 0.015 inches.

[0059] An important aspect of the present invention is that the aluminumsheet product that is produced in accordance with the present inventioncan maintain sufficient strength and formability properties while havinga relatively thin gauge. This is important when the aluminum sheetproduct is utilized in making drawn and ironed containers. The trend inthe can-making industry is to use thinner aluminum sheet stock for theproduction of drawn and ironed containers, thereby producing a containercontaining less aluminum and having a reduced cost. However, to usethinner gauge aluminum sheet stock the aluminum sheet stock must stillhave the required physical characteristics, as described in more detailbelow. Surprisingly, a continuous casting process has been discoveredwhich, when utilized with the alloys of the present invention, producesan aluminum sheet stock that meets the industry standards.

[0060] The aluminum alloy sheet produced according to the preferredembodiment of the present invention is useful in a number ofapplications including, but not limited to, drawn and ironed containerbodies. When the aluminum alloy sheet is to be fabricated into drawn andironed container bodies, the alloy sheet preferably has an after-bakeyield strength of at least about 37 ksi, more preferably at least about38 ksi, and more preferably at least about 40 ksi. After-bake yieldstrength refers to the yield strength of the aluminum sheet after beingsubjected to a temperature of about 400° F. for about 10 minutes. Thistreatment simulates conditions experienced by a container body duringpost-formation processing, such as the washing and drying of containers,and drying of films or paints applied to the container. Preferably, theas rolled yield strength is at least 38 ksi and more preferably at least39 ksi, and preferably is not greater than about 44 ksi and morepreferably is not greater than about 43 ksi. The aluminum sheetpreferably has an after bake ultimate tensile strength of at least about40 ksi, more preferably at least about 41.5 ksi and more preferably atleast about 43 ksi. The as rolled ultimate tensile strength ispreferably at least 41 ksi and more preferably at least 42 ksi and morepreferably at least 43 ksi, and preferably, not greater than 46 ksi andmore preferably not greater than 45 ksi and more preferably not greaterthan 44.5 ksi.

[0061] To produce acceptable drawn and ironed container bodies, aluminumalloy sheet should have a low earing percentage. A typical measurementfor earing is the 45° earing or 45° rolling texture. Forty-five degreesrefers to the position on the aluminum sheet which is 45° relative tothe rolling direction. The value for the 45° earing is determined bymeasuring the height of the ears which stick up in a cup, minus theheight of valleys between the ears. The difference is divided by theheight of the valleys times 100 to convert to a percentage.

[0062] Preferably, the aluminum alloy sheet, according to the presentinvention, has a tested earing of less than about 2 percent and morepreferably less than about 1.8 percent. Importantly, the aluminum alloysheet product produced in accordance with the present invention shouldbe capable of producing commercially acceptable drawn and ironedcontainers. Therefore, when the aluminum alloy sheet product isconverted into container bodies, the earing should be such that thebodies can be conveyed on the conveying equipment and the earing shouldnot be so great as to prevent acceptable handling and trimming of thecontainer bodies.

[0063] In addition, the aluminum sheet should have an elongation of atleast about 2 percent and more preferably at least about 3 percent andmore preferably at least about 4 percent. Further, container bodiesfabricated from the alloy of the present invention having a minimum domereversal strength of at least about 88 psi and more preferably at leastabout 90 psi at current commercial thickness.

[0064] In yet another embodiment of the present invention, a process andalloy composition for producing aluminum alloy sheet having goodstrength and forming properties is provided. As in the previousembodiment, the resulting aluminum alloy sheet is particularly suitablefor the fabrication of drawn and ironed articles, such as containers.The resulting sheet can have reduced earing and improved strength inthinner gauges relative to comparable sheet fabricated according to theprior art.

[0065] The composition of the aluminum alloy sheet is important torealize these desirable properties. In one embodiment, the aluminumalloy composition includes the following constituents:

[0066] (i) manganese, preferably with a minimum of at least about 0.7 wt% manganese and more preferably with a minimum of at least about 1.05 wt% manganese, and preferably with a maximum of at most about 1.3 wt %manganese and more preferably with a maximum of at most about 1.07 wt %manganese;

[0067] (ii) magnesium, preferably with a minimum of at least about 1.0wt % magnesium and more preferably with a minimum of at least about 1.35wt % magnesium and preferably with a maximum of at most about 1.6 wt %magnesium and more preferably with a maximum of at most about 1.50 wt %magnesium;

[0068] (iii) copper, preferably with a minimum of at least about 0.3 wt% copper and more preferably with a minimum of at least about 0.45 wt %copper, and preferably with a maximum of at most about 0.6 wt %. copperand more preferably with a maximum of at most about 0.50 wt % copper;

[0069] (iv) iron, preferably with a minimum of at least about 0.3 wt %iron and more preferably with a minimum of at least about 0.55 wt % ironand preferably with a maximum of at most about 0.7 wt % iron and morepreferably with a maximum of at most about 0.60 wt % iron; and

[0070] (v) silicon, preferably of no more than about 0.5 wt % siliconand more preferably with a minimum of at least about 0.39 wt %; silicon,and a maximum of at most about 0.45 wt % silicon.

[0071] The balance of the alloy composition consists essentially ofaluminum and incidental additional materials and impurities. Theincidental additional materials and impurities are preferably limited toabout 0.05 wt % each, and the sum total of all incidental additionalmaterials and impurities preferably does not exceed about 0.15 wt %.

[0072] The alloy composition differs from prior art compositions in anumber of respects. By way of example, the alloy has relatively highmagnesium, copper, iron, and silicon content. While not wishing to bebound by any theory, it is believed that the high magnesium, copper, andiron content significantly enhance the sheet's yield and tensilestrengths, and the silicon content causes alpha transformation particlesto be larger. The use of larger alpha phase particles reduces gallingand scoring of containers by inhibiting the accumulation of metalresidue on the canmaking dies. Copper not only increases strengthproperties but also retards after-bake property drops. Iron increasesstrength properties and maintains a desired grain size.

[0073] With continuing reference to FIG. 2, in the process a cast stripis produced in a casting cavity (e.g., a block caster, a belt caster, atwin-roll caster, etc.) and subjected to hot milling as describedpreviously to form the hot rolled sheet. The hot mill preferably reducesthe thickness of the cast strip in one or more passes by at least about700 and more preferably by at least about 80%. The gauge of the caststrip preferably ranges from about 0.50 inches to about 0.75 incheswhile the gauge of the hot rolled sheet ranges from about 0.060 to about0.110 inches. The hot rolled sheet preferably exits the hot mill at atemperature ranging from about 500 to about 750° F. It is preferred thatthe total reduction of the cast strip be realized in two to three passeswith two passes being most preferred.

[0074] The hot rolled sheet passes directly to a cooling step before thefirst cold rolling step. The hot rolled sheet is allowed to cool beforecold rolling to a temperature less than the recrystallizationtemperature of the hot rolled sheet. Preferably, the hot rolled sheet isallowed to cool for a sufficient period of time to produce a hot rolledsheet having a temperature ranging from about 75 to about 140° F.Generally, the hot rolled sheet is about 48 hours. The sheet ispreferably not quenched or otherwise solution heat treated.

[0075] In the cold rolling step, the cooled hot rolled sheet is passedbetween cold rollers, as necessary, to form a cold rolled sheet at anintermediate gauge. Preferably, the intermediate gauge ranges from about0.050 to about 0.080 inches and more preferably from about 0.055 toabout 0.075 inches. It is preferred that the thickness of the sheet bereduced in total by less than 65%, more preferably by from about 35% toabout 60%, and most preferably by from about 30% to about 55% throughthe cold rollers. It is preferred that the total sheet reduction berealized in two passes or less, with a single pass being most preferred.

[0076] When the desired intermediate anneal gauge is reached followingthe first cold rolling step, the cold rolled sheet is breakdown or firstannealed in a continuous or batch anneal oven to form an intermediatecold mill anneal sheet and reduce the residual cold work and lower theearing of the aluminum sheet. The intermediate anneal is preferably aheat soak anneal. Preferably, the sheet is intermediate annealed at aminimum temperature of at least about 700° F. and more preferably at aminimum of at least about 800° F., and preferably at a maximumtemperature of about 900° F. and most preferably at a maximumtemperature of about 850° F. The most preferred annealing temperature isabout 825° F. The annealing time is preferably a minimum of at leastabout 0.5 hours and is more preferably a minimum of at least about 1hour with about 3 hours being most preferred.

[0077] Preferably, the intermediate annealed sheet is allowed to cool toa temperature less than the recrystallization temperature of the sheetprior to additional cold rolling steps. The preferred temperature forcold rolling ranges from about 75 to about 140 ° F. The cooling timetypically is 48 hours. As will be appreciated, the sheet can be forcecooled in a significantly shorter time by injecting nitrogen gas intothe batch anneal oven to reduce the sheet temperatures to about 250° F.However, the sheet is preferably not subjected to solution heattreatment.

[0078] After the intermediate cold mill annealed sheet has cooled toambient temperature, a further cold rolling step is used, as necessary,to form a further cold rolled sheet having a smaller intermediate gauge.Preferably, the intermediate gauge ranges from about 0.015 to about0.040 inches and more preferably from about 0.020 to about 0.030 inches.Preferably, the thickness of the strip is reduced in total by less than65%, more preferably by from about 35% to about 60%, and most preferablyfrom about 50% to about 60% in the step. It is preferred that the totalreduction be realized in two passes or less, with a single pass beingpreferred.

[0079] The further cold rolled sheet is annealed a second time,preferably in a continuous or batch anneal oven, to form a furtherintermediate cold mill annealed sheet. The anneal is preferably a heatsoak anneal. Preferably, the annealing temperature ranges from about 600to about 900° F., more preferably from about 650 to about 750° F. Themost preferred temperature is about 705° F. The annealing timepreferably is at least about 0.5 hrs and more preferably about 2 hrs,with about 3 hrs being most preferred.

[0080] Preferably, the further intermediate cold mill annealed sheet isallowed to cool to a temperature less than the recrystallizationtemperature of the sheet prior to the final cold rolling step. Thepreferred temperature for cold rolling ranges from about 75 to about140° F. The cooling time typically is about 48 hours. As will beappreciated, the sheet can be force cooled in a significantly shortertime by injecting the nitrogen gas into the batch annealing oven toreduce the sheet temperatures to about 250° F. However, the sheet ispreferably not subjected to solution heat treatment.

[0081] Finally, a final cold rolling step is used to impart the finalproperties to the sheet. Generally, the final gauge is specified andtherefore the desired percent reduction for the final cold rolling stepis determined. The percent reductions in the other cold rolling stepsand the hot rolling step are back calculated based upon the finaldesired gauge. The back calculation is performed such that the totalcold mill reductions before the first annealing step, between the firstand second annealing steps, and after the second annealing step are eachless than about 65%.

[0082] In a preferred embodiment, the total reduction to final gauge isfrom about 40% to 65%, more preferably from about 50% to about 60% andmost preferably from about 55% to about 60% in the step. Preferably, thereduction is realized through a single pass. When the sheet isfabricated for drawn and ironed container bodies, the final gauge canbe, for example, from about 0.010 to about 0.014 inches. The final coldrolling step is preferably conducted at a temperature ranging from about75° F. to about 120° F.

[0083] The aluminum alloy sheet produced from the above-noted alloy bythis process is especially useful for drawn and ironed container bodies.When the aluminum alloy sheet is to be fabricated into drawn and ironedcontainer bodies, the alloy sheet preferably has an as-rolled yieldtensile strength of at least about 38.5 ksi, more preferably at leastabout 39.0 ksi, and most preferably at least about 39.5 ksi. The maximumas-rolled yield tensile strength is no more than about 40.0 ksi.Preferably, the after-bake yield tensile strength is at least about 37.0ksi, more preferably at least about 38.0 ksi, and most preferably is atleast about 39.0 ksi, and preferably is not greater than about 39.5 ksi.The aluminum alloy sheet preferably has an as-rolled ultimate tensilestrength of at least about 42.5 ksi, more preferably at least about 43.0ksi and most preferably at least about 43.5 ksi and preferably less thanabout 44.0 ksi. The after-bake ultimate tensile strength is preferablyat least about 42.5 ksi, more preferably at least about 43.0 ksi andmost preferably at least about 43.5 ksi, and preferably not greater thanabout 44.0 ksi. Preferably, the aluminum alloy sheet has an earing ofless than about 2%, more preferably less than about 1.8% and mostpreferably less than about 1.6%. The earing typically ranges from about1.5% to about 1.7%. The sheet preferably has an after-bake elongation ofat least about 4.5, more preferably at least about 5.0% and mostpreferably at least about 5.5%. The sheet preferably has an as-rolledelongation of at least about 4.0%, more preferably at least about 4.5%,and most preferably at least about 5.0%. Further, container bodiesfabricated from the alloy of the present invention have a minimum domereversal strength of at least about 90 psi and more preferably at leastabout 95 psi at current commercial thickness.

[0084] In a further embodiment, the aluminum alloy composition includesthe following constituents:

[0085] (i) manganese, preferably with a minimum of at least about 0.95wt % manganese and preferably with a maximum of at most about 1.1 wt %manganese;

[0086] (ii) magnesium, preferably with a minimum of at least about 1.3wt % magnesium and preferably with a maximum of at most about 1.5 wt %magnesium;

[0087] (iii) copper, preferably with a minimum of at least about 0.43 wt% copper and a maximum of at most about 0.50 wt % copper;

[0088] (iv) iron, preferably with a minimum of at least about 0.51 wt %iron and a maximum of at most about 0.60 wt % iron;

[0089] (v) silicon, preferably with a minimum of about 0.37 wt % siliconand a maximum of at most about 0.45 wt % silicon.

[0090] The balance of the alloy composition consists essentially ofaluminum and incidental additional materials and impurities. Theincidental additional materials and impurities are preferably limited toabout 0.05 wt % each, and the sum total of all incidental materials andimpurities preferably does not exceed about 0.15 wt %.

EXAMPLES 1-10

[0091] In order to illustrate the advantages of the present invention, anumber of aluminum alloys were formed into sheets.

[0092] Four examples comparing AA 3004/3104 alloys with the alloys ofthe present invention are illustrated in Table I. TABLE I CompositionHot mill Cold mill (weight %) Anneal Anneal Secondary Example Mg Mn CuFe Temperature Temperature Cold Work 1 (comparative) 1.21 0.84 0.22 0.44825° F. 705° F. 75% 2 (comparative) 1.28 0.96 0.21 0.41 825° F. 705° F.75% 3 1.22 0.83 0.42 0.35 825° F. 705° F. 64% 4 1.31 0.99 0.41 0.34 825°F. 705° F. 61%

[0093] In each example, the silicon content was between 0.18 and 0.22and the balance of the composition was aluminum. Each alloy wascontinuously cast in a block caster and was then continuously hotrolled. The hot mill and intermediate cold mill anneals were each forabout 3 hours. After the hot mill anneal; the sheets were cold rolled toreduce the thickness by from about 45 to 70 percent in one or morepasses. After this cold rolling, the sheets were intermediate cold millannealed at the temperature indicated.

[0094] Thereafter, the sheets were cold rolled to reduce the thicknessby the indicated percentage. Table II illustrates the results of testingthe processed sheets. TABLE II As-Rolled After-Bake Example UTS YSElongation Earing UTS YS Elongation 1 (comparative) 41.3 39.3 3.2% 2.2%40.0 35.2 4.8% 2 (comparative) 43.2 40.4 3.1% 2.2% 40.7 36.0 4.3% 3 42.439.4 3.2% 1.4% 42.3 37.1 5.1% 4 43.1 40.1 3.2% 1.2% 43.3 37.8 5.3%

[0095] The ultimate tensile strength (UTS), yield strength (YS),elongation, and earing were each measured when the sheet was in theas-rolled condition. The UTS, YS and elongation were then measured aftera bake treatment which consisted of heating the alloy sheet to about400° F. for about 10 minutes.

[0096] Comparative Examples 1 and 2 illustrate that, when fabricatedusing a continuous caster, an AA 3004/3104 alloy composition is too weakfor can-making applications. In order to achieve similar as-rolledstrengths, the 3004/3104 alloy requires more cold work, and therefore,has higher earing. Further, the 3004/3104 alloy has a large drop inyield strength after the bake treatment, which can result in a low domereversal strength for the containers.

[0097] Examples 3 and 4 illustrate alloy compositions according to thepresent invention. The sheets had a significantly lower drop in yieldstrength due to baking and therefore maintained adequate strength forcan-making applications. Further, these alloy sheets maintained lowearing. These examples substantiate that AA3004/3104 alloys that areprocessed in a continuous caster are too weak for use as containers,particularly for carbonated beverages. However, when the copper level isincreased according to the present invention, the sheet has sufficientstrength for forming cans.

[0098] To further illustrate the advantages of the present invention, anumber of examples were prepared to demonstrate the effect of increasedthermal treatment temperature, such as at temperatures taught by theprior art. These examples are illustrated in Table III. TABLE IIIComposition Hot mill Example Mg Mn Cu Fe Anneal Result 5 1.28 0.98 0.420.35 1000° F. Unable to unwrap  3 hours coils 6 1.28 0.98 0.42 0.35 950° F. Unable to unwrap  3 hours coils 7 1.28 0.98 0.42 0.35  925° F.Unable to unwrap 10 hours 4 of 5 coils

[0099] As is illustrated in Table III, annealing temperatures at 925° F.or higher resulted in welded coils which were not able to be unwrappedfor further processing. As a result, such temperatures are clearly notuseful for alloy sheets according to the present invention.

[0100] Table IV illustrates the effect of increasing the iron contentaccording to a preferred embodiment of the present invention. TABLE IVComposition Hot mill Intermediate (weight %) Anneal Cold mill AnnealExample Mg Mn Cu Fe Temperature Temperature 8 1.22 0.83 0.42 0.38 825°F. 705° F. 9 1.31 0.94 0.42 0.36 825° F. 705° F. 10  1.37 1.12 0.42 0.55825° F. 705° F.

[0101] In each example in addition to the listed elements, the siliconcontent was between 0.18 and 0.23 and the balance was essentiallyaluminum. Each alloy was cast in a block caster and was thencontinuously hot rolled. The hot mill anneal in all cases was for about3 hours. After the hot mill anneal, the sheets were cold rolled toreduce the thickness by from about 45 to 70 percent in one or morepasses. After this cold rolling, the sheets were intermediate cold millannealed for about 3 hours at the temperatures indicated and thenfurther cold rolled.

[0102] Table V illustrates the results of testing the foregoing aluminumalloy sheets. TABLE V UTS YS Elongation Earing Example (ksi) (ksi) % %Result 8 42.3 37.0 5.0 1.5 Excellent for 5.5 oz. cans 9 43.2 38.2 4.81.6 Made 12 oz. cans 10  43.2 37.8 5.2 1.7 Excellent for 12 oz. cans

[0103] The ultimate tensile strength (UTS), yield strength (YS) andelongation were measured after a bake treatment which consisted ofheating the alloy to about 400° F. for about 10 minutes.

[0104] Example 8 illustrates an alloy and process according to thepresent invention for making a sheet product which is sufficient for 5.5ounce can bodies. By increasing the copper content and maintaining anadequate cold mill anneal temperature, sheet is produced that isexcellent for the commercial production of 5.5 ounce container bodies.However, the sheet did not have sufficient formability for thecommercial production of 12 ounce container bodies. Although the sheethad sufficient strength and 12 ounce container bodies were made, acommercially unacceptable number of the 12 ounce container bodies wererejected when produced on two commercial can-lines.

[0105] Example 9 is similar to Example 8, with increased magnesium andmanganese; the sheet was also useful for 5.5 ounce container bodies anddid produce some 12 ounce container bodies with acceptable strength.However, the 12 ounce container bodies also had a commerciallyunacceptable number of rejects.

[0106] Example 10 illustrates that by increasing the iron contentaccording to the present invention, this problem can be overcome. InExample 10, the sheet material had excellent fine grain size and wasused to produce 12 ounce container bodies on two commercial containerlines with a commercially acceptable rate of rejection.

[0107] In an alternative embodiment of the present invention, fine grainsize may be imparted to the sheet material by using a continuousintermediate cold mill anneal. In one example, an aluminum alloy sheethaving the composition illustrated for Example 4 was intermediate coldmill annealed in a continuous, gas-fired furnace wherein the metal wasexposed to a peak temperature of about 900° F. This treatment imparted avery fine grain size to the sheet. The sheet had an ultimate tensilestrength of 45.5 ksi and 12 ounce container bodies were produced thatmet commercial strength requirements.

EXAMPLES 11-19

[0108] To illustrate the advantages of aluminum alloy sheet of thepresent invention relative to aluminum alloy sheet produced by othercontinuous casting and ingot casting processes, a number of aluminumalloys were formed into sheets. In the tests, six samples of 3000 seriesalloys produced by other continuous casting or ingot casting processeswere compared with three 3000 series alloys produced according to themethod of the present invention. The results are presented in Tables VI(A) and (B). TABLE VI(A) Alloy Composition As rolled After Bake Sample #Designation Si Cu Fe Mn Mg UTS YTS Elong. Earing % UTS YTS EL 11 5349D0.38 0.43 0.28 1.14 1.81 42.8 39.5 3.2 1.4 42.5 37.2 5.6 12 3304B 0.190.37 0.41 0.81 1.2 42.3 38.8 4.1 1.7 42.3 37.1 5.1 13 3304C 0.21 0.550.41 1.04 1.3 43.9 39.9 4.4 1.8 43.1 37.8 5.3 14 3304F 0.21 0.55 0.410.83 1.36 43.3 39.1 4.4 1.8 42.6 37.3 5.3 15 3304CSV 0.38 0.57 0.47 1.051.33 43.5 40.1 4.59 2.6 43.3 37.6 5.87 16 3304C5V(mod) 0.38 0.57 0.461.04 1.35 42.8 38.9 4.99 1.7 42 36.3 5.58 17 3304CJ(mod) 0.42 0.598 0.51.06 1.42 43.2 39.3 4.7 1.6 42.7 37 5.8 18 3304CJ(mod) 0.42 0.59 0.51.03 1.448 43.25 39.6 4.6 1.7 42.7 37 5.7 19 Comparative AA3004 44.140.08 6.74 1.8 41.1 37.28 5.88

[0109] TABLE VI(B) Total cold roll red % from first Hot mill Total coldroll red anneal point to anneal % to (first) anneal Cold mill firstsecond anneal Cold mill second Total final cold Sample # temp pointanneal temp point anneal temp mill red % 11 825 74 N/A N/A 705 45 12 82553 N/A N/A 705 65 13 825 75 N/A N/A 705 60 14 825 75 N/A N/A 705 60 15825 74 N/A N/A 705 60 16 N/A 41 825 60 705 55 17 N/A 33 825 60 705 55 18N/A 42 825 60 705 55 19 620 F. self 91% total cold work to finish gaugeanneal

[0110] The balance of the composition in each sample was aluminum.Samples 11-18 were continuously cast in a block caster and thencontinuously hot rolled. Samples 11-15 were annealed, cold rolled,annealed a second time, and cold rolled to form the aluminum alloysheet. In accordance with the process of the present invention, samples16-18 were cold rolled, annealed, cold rolled, annealed, and cold rolledto form the aluminum alloy sheet. The various anneals were each forabout 3 hours. Samples 11, 13-16, and 19 were fabricated into cans onconventional canmaking equipment and the canmaking behavior of thesamples determined.

[0111] Table VII illustrates the results of testing the processedsheets. TABLE VII BODYSTOCK PRODUCT PROGRESSION SAM- NECKING/ PLE ALLOYSCORING BUCKLE FLANGE EARING 11 5349D Severe Fair Very Poor 1.7% 133304C Severe Good Poor 2.4% 14 3304F Fair Fair Fair 2.4% 15 3304 CSVGood Good Fair 2.6% 16 3304 (MOD) Good Good Good 1.7% 19 Comparative2.0%

[0112] Samples 11 and 13-14 produced scored cans and demonstrated poornecking/flange behavior. Samples 11 and 14 further demonstrated a fairbuckle strength while sample 13 demonstrated poor earing. Sample 14exhibited fair qualities in can scoring, buckle strength, andnecking/flange behavior but a very poor earing. In sharp contrast,sample 16, which was fabricated by the process of the present inventionhad a low degree of can scoring and acceptable buckle strength,necking/flange behavior, and earing. Sample 19, which was produced byingot casting techniques and is considered high quality canmaking stock,in fact had a higher earing than sample 16.

[0113] Samples 15 and 16 were compared to sample 19, which is highquality canmaking sheet prepared by ingot casting techniques. Thevarious sheet samples were formed into cans. The results are presentedin Table VIII below. TABLE VIII BODYMAKER After-Deco/IBO Ovens UTS YTSElong. UTS YTS Elong. SAMPLE ALLOY (ksi) (ksi) (%) (ksi) (ksi) (%) 153304 CSV 51.10 47.50 0.90 47.00 40.10 2.90 16 3304 CSV 48.95 45.66 1.0844.34 38.43 3.76 (modified) 19 (Com- 3004/3104 48.96 45.06 1.63 43.2538.67 3.82 parative)

[0114] The ultimate tensile strength (UTS), yield tensile strength(YTS), and elongation (Elong) were measured after the container exitedthe bodymaker and after the container exited the deco step. The decostep or after bake step included heating the alloy sheet to about 400°F. for about 10 minutes. The body maker samples are the mechanicalproperties of the container thick wall in a transverse direction.

[0115] Sample 15 exhibited a greater UTS and YTS and lower elongationthan sample 16 after the bodymaker and the after-deco step. Sample 16exhibited more elongation than sample 15, especially after the decostep. In fact, the properties of sample 16 mirrored the properties ofsample 19, which, as noted above, is considered high quality canmakingstock, in both UTS and YTS after the bodymaker and deco step and inelongation after the deco step. The differences in physical propertiesof samples 16 and 19 in each of these categories were within testingerror of one another. Sample 19, however, did have a measurably higherelongation than sample 16 after the bodymaker. Nonetheless, sample 16has canmaking properties similar to sample 19. This is a surprising andunexpected result for continuously cast aluminum alloy sheet which hassignificantly more cold work than ingot cast sheet.

[0116] While various embodiments of the present invention have beendescribed in detail, it is apparent that modifications and adaptationsof those embodiments will occur to those skilled in the art. It is to beexpressly understood that such modifications and adaptations are withinthe spirit and scope of the present invention.

We claim:
 1. A system for fabricating an aluminum sheet product,comprising the steps of: (a) casting means for continuously casting analuminum alloy melt to form a cast strip; (b) hot rolling means for hotrolling the cast strip to form a hot rolled sheet; (c) first coldrolling means for cold rolling said hot rolled sheet to form a coldrolled sheet; (d) first annealing means for annealing said cold rolledsheet to form an intermediate cold mill annealed sheet; (e) second coldrolling means for cold rolling said intermediate cold mill annealedsheet to form a further cold rolled sheet; (f) second annealing meansfor annealing the further cold rolled sheet to form a further cold millannealed sheet; and (g) third cold rolling means for cold rolling thefurther cold mill annealed sheet to form aluminum alloy sheet.
 2. Asystem as recited in claim 1, wherein said hot rolling means performshot rolling in the absence of homogenization.
 3. A system as recited inclaim 1, wherein said hot rolling means reduces the gauge of said caststrip by at least about 70 percent.
 4. A system as recited in claim 1,wherein said first cold rolling means reduces the gauge of said hotrolled sheet by less than about 65%.
 5. A system as recited in claim 1,wherein said first cold rolling means performs cold rolling in theabsence of annealing of the hot rolled sheet.
 6. A system as recited inclaim 1, wherein said second cold rolling means reduces the gauge of theintermediate cold mill annealed sheet by no more than about 65%.
 7. Asystem as recited in claim 1, wherein the temperature at which saidfirst annealing means performs annealing ranges from about 700 to about900° F.
 8. A system as recited in claim 1, wherein said aluminum alloymelt comprises at least about 75 weight percent scrap.
 9. A system asrecited in claim 1, wherein said aluminum alloy melt comprises: (i) fromabout 0.7 to about 1.3 weight percent manganese, (ii) from about 1 toabout 1.6 weight percent magnesium, (iii) from about 0.3 to about 0.6weight percent copper, (iv) no more than about 0.50 weight percentsilicon, and (v) from about 0.3 to about 0.7 weight percent iron, thebalance being aluminum and incidental additional materials andimpurities.
 10. A system as recited in claim 1, wherein the third coldrolling means reduces the gauge of the further cold mill annealed sheetby less than about 75%.
 11. A system for fabricating an aluminum sheetproduct, comprising the steps of: (a) continuous casting means forcontinuously strip casting an aluminum alloy melt to form a cast strip;(b) hot rolling means for hot rolling said cast strip in the absence ofhomogenization of said cast strip to form a hot rolled sheet; (c) firstcold rolling means for cold rolling said hot rolled sheet to form a coldrolled sheet; (d) first annealing means for annealing said cold rolledsheet to form an intermediate cold mill annealed sheet; (e) second coldrolling means for cold rolling said intermediate cold mill annealedsheet to form a further cold rolled sheet, wherein the reduction ingauge of the intermediate cold mill annealed sheet is less than about65%; (f) second annealing means for annealing the further cold rolledsheet to form a further cold mill annealed sheet, and (g) third coldrolling means for cold rolling said further cold mill annealed sheet toform aluminum alloy sheet, wherein the reduction in gauge of the furthercold mill annealed sheet is less than about 65%.
 12. A system as recitedin claim 11, wherein said aluminum alloy melt comprises: (i) from about0.7 to about 1.3 weight percent manganese, (ii) from about 1 to about1.6 weight percent magnesium, (iii) no more than about 0.5 weightpercent silicon, and (iv) from about 0.3 to about 0.7 weight percentiron, the balance being aluminum and incidental additional materials andimpurities.
 13. A system as recited in claim 11, wherein the thicknessof the aluminum alloy sheet is at least about 40% of the thickness ofthe hot rolled sheet.
 14. A system as recited in claim 11, wherein thethickness of the hot rolled sheet is no more than about 30% of thethickness of said cast strip.
 15. A system for fabricating an aluminumsheet product, comprising the steps of: (a) continuous casting means forcontinuously casting an aluminum alloy melt to form a cast strip; (b)first cold rolling means for cold rolling said cast strip to form a coldrolled sheet; (c) first annealing means for annealing said cold rolledsheet to form an intermediate cold mill annealed sheet, wherein theannealing temperature ranges from about 700 to about 900° F.; (d) secondcold rolling means for cold rolling said intermediate cold mill annealedsheet to form a further cold rolled sheet; (e) second annealing meansfor annealing the further cold rolled sheet to form a further cold millannealed sheet; and (f) third cold rolling means for cold rolling thefurther cold mill annealed sheet to form aluminum alloy sheet.
 16. Asystem as recited in claim 15, further comprising hot rolling means forhot rolling the cast strip and wherein the hot rolling is performed inthe absence of homogenization.
 17. A system as recited in claim 16,wherein said hot rolling means reduces the gauge of said cast strip byat least about 70 percent.
 18. A system as recited in claim 16, whereinsaid first cold rolling means reduces the gauge of said hot rolled sheetby less than about 65%.
 19. A system as recited in claim 16, whereinsaid first cold rolling means performs cold rolling in the absence ofannealing of the hot rolled sheet.
 20. A system as recited in claim 15,wherein said second cold rolling means reduces the gauge of theintermediate cold mill annealed sheet by no more than about 65%.
 21. Asystem as recited in claim 15, wherein said aluminum alloy meltcomprises at least about 75 weight percent scrap.
 22. A system asrecited in claim 15, wherein said aluminum alloy melt comprises: (i)from about 0.7 to about 1.3 weight percent manganese, (ii) from about 1to about 1.6 weight percent magnesium, (iii) from about 0.3 to about 0.6weight percent copper, (iv) no more than about 0.50 weight percentsilicon, and (v) from about 0.3 to about 0.7 weight percent iron, thebalance being aluminum and incidental additional materials andimpurities.
 23. A system as recited in claim 15, wherein the third coldrolling means reduces the gauge of the further cold mill annealed sheetby less than about 75%.
 24. A method for fabricating aluminum alloysheet, comprising: (a) continuously casting an aluminum alloy melt in acontinuous caster to form a cast strip having a cast output temperature;(b) heating the cast strip to a heated temperature, wherein the heatedtemperature is above the recrystallization temperature of the caststrip; (c) hot rolling the cast strip to form a hot rolled strip; (d)recrystallizing at least one of the cast and hot rolled strips; and (e)further treating the hot rolled strip to form aluminum alloy sheet. 25.A method as recited in claim 24, wherein the aluminum alloy meltcomprises from about 1 to about 1.6 weight percent magnesium.
 26. Amethod as recited in claim 24, wherein said aluminum alloy meltcomprises at least about 75 weight percent scrap.
 27. A method asrecited in claim 25, wherein said aluminum alloy melt comprises: (i)from about 0.7 to about 1.3 weight percent manganese; (ii) from about0.3 to about 0.6 weight percent copper; (iii) no more than about 0.50weight percent silicon; and, (iv) from about 0.3 to about 0.7 weightpercent iron, the balance being aluminum and incidental additionalmaterials and impurities.
 28. The method as recited in claim 24, whereinthe recrystallization temperature is 20 above about 432 degrees Celsius.29. The method as recited in claim 24, wherein the recrystallizationtemperature ranges from about 432 degrees Celsius to about 565 degreesCelsius.
 30. A system for fabricating an aluminum sheet product,comprising the steps of: (a) a continuous caster that continuously castsan aluminum alloy melt to form a cast strip; (b) a heater that heats thecast strip to a heated temperature, wherein the heated temperature isabove the recrystallization temperature of the cast strip; and (c) a hotroller that hot rolls the heated cast strip to form a rolled sheet. 31.The method recited in claim 30, wherein said aluminum alloy meltcomprises a weight percent of aluminum ranging from about 95 to about 98percent.
 32. The method recited in claim 30, wherein said aluminum alloymelt comprises: (i) from about 0.7 to about 1.3 weight percentmanganese; (ii) from about 1 to about 1.6 weight percent magnesium;(iii) from about 0.3 to about 0.6 weight percent copper; (iv) no morethan about 0.50 weight percent silicon; and, (v) from about 0.3 to about0.7 weight percent iron, the balance being aluminum and incidentaladditional materials and impurities.
 33. The method recited in claim 30,wherein the rolling means reduces the gauge of the sheet by less thanabout 65%.
 34. A method for fabricating aluminum alloy sheet,comprising: (a) continuously casting an aluminum alloy melt in acontinuous caster to form a cast strip; (b) rolling the cast strip toform a rolled sheet; and, (c) annealing said rolled sheet by impartingelectromagnetic energy to the rolled sheet to form the aluminum alloysheet.
 35. The method recited in claim 34, wherein said aluminum alloymelt comprises a weight percent of aluminum ranging from about 95 toabout 98 percent.
 36. The method recited in claim 34, wherein saidaluminum alloy melt comprises: (i) from about 0.7 to about 1.3 weightpercent manganese; (ii) from about 1 to about 1.6 weight percentmagnesium; (iii) from about 0.3 to about 0.6 weight percent copper; (iv)no more than about 0.50 weight percent silicon; and, (v) from about 0.3to about 0.7 weight percent iron, the balance being aluminum andincidental additional materials and impurities.
 37. The method recitedin claim 34, wherein the rolling means reduces the gauge of the sheet byless than about 65%.
 38. A system for fabricating aluminum alloy sheet,comprising: (a) a continuous caster that continuously casts an aluminumalloy melt to form a cast strip; (b) a rolling mill that rolls the caststrip to form a rolled sheet; and, (c) an induction heater that annealssaid rolled sheet to form the aluminum alloy sheet.
 39. The systemrecited in claim 38, wherein said aluminum alloy melt comprises a weightpercent of aluminum ranging from about 95 to about 98 percent.
 40. Thesystem recited in claim 38, wherein said aluminum alloy melt comprises:(i) from about 0.7 to about 1.3 weight percent manganese; (ii) fromabout 1 to about 1.6 weight percent magnesium; (iii) from about 0.3 toabout 0.6 weight percent copper; (iv) no more than about 0.50 weightpercent silicon; and, (v) from about 0.3 to about 0.7 weight percentiron, the balance being aluminum and incidental additional materials andimpurities.
 41. The system recited in claim 38, wherein the rollingmeans reduces the gauge of the sheet by less than about 65%.
 42. Asystem for fabricating an aluminum alloy sheet, comprising: (a) castingmeans for continuously casting an aluminum alloy melt having a weightpercent of aluminum ranging from about 95 percent to about 98 percent toform a cast strip; and, (b) rolling means for rolling said cast strip toform a rolled sheet; (c) induction heating means for inductively heatingsaid rolled sheet to form the aluminum alloy sheet.
 43. The systemrecited in claim 42, wherein said aluminum alloy melt comprises: (i)from about 0.7 to about 1.3 weight percent manganese; (ii) from about 1to about 1.6 weight percent magnesium; (iii) from about 0.3 to about 0.6weight percent copper; (iv) no more than about 0.50 weight percentsilicon; and, (v) from about 0.3 to about 0.7 weight percent iron, thebalance being aluminum and incidental additional materials andimpurities.
 44. The system recited in claim 42, wherein the rollingmeans reduces the gauge of the sheet by less than about 65%.